Disconnecting switch with surge protection gaps



Jan. 7, 1964 J. B. OWENS 3,117,192

DISCONNECTING SWITCH WITH suns: PROTECTION GAPS Filed Feb. 15, 1961United States Patent 3,117,192 DISCONNECTING SWITCH WITH SURGEPROTECTION GAPS James B. Owens, Greensburg, Pa., assignor to I-T-ECircuit Breaker Company, Philadelphia, Pa., a corporation ofPennsylvania Filed Feb. 13, 1961, Ser. No. 88,828 3 Claims. (Cl. 200-48)My invention relates to high voltage disconnecting switches, and morespecifically relates to the provision of electrodes at either end of theswitch which are spaced from the switch open gap formed when the switchis in its open position.

Disconnecting switches are designed to isolate electrical apparatus andportions of electric systems from energized lines for safe handling,maintenance and repair. In order to insure adequate protection forpersonnel working on the disconnected equipment, the switch open gapmust be adequate to withstand all normal and abnormal voltages impressedupon it by the system. If a surge voltage causes the switch open gap toflash over, the life of personnel may be endangered.

Disconnecting switches are customarily designed so that the switch opengap will withstand more voltage than the insulator units which supportthe energized parts from the grounded metal base. With thisconstruction, surge voltages will normally create fiashovers between theenergized parts and ground instead of across the open switch gap. Thus,the insulator units provide surge protection for the switch andoperating personnel. With the design, it is necessary to use large gapopenings in the switch in order to insure a greater withstand abilitythan exists across the insulator units.

Switch insulators may exhibit a very high withstand ability especiallywhen subjected to negative polarity impulse voltages. It has been foundthat by placing rod gap electrodes on the base of the insulator units,the negative impulse withstand ability can be lowered withoutsignificantly affecting other electrical characteristics. Gaps of thistype have been used as surge protection on switch insulators to enablethe use of shorter switch open gaps with a corresponding economy inswitch construction. However, in previously used structures, the gapshave been located in such a position that the arcing attendant to a gapoperation could interfere with the integrity of the switch open gapinsulation so that the switch open gap must still be relatively long.

I have invented a new and novel gap arrangement which locates the gapelectrodes in a position such that gap flashover will properly protectthe switch open gap and maintain its full insulation.

Thus, the switch open gap can be smaller to thereby effect a substantialsaving in the length of the switch blade, and the length of the base.This, in turn, permits the use of lighter, and less expensiveinsulators, whereby there is a substantial overall saving in weight andexpense while still retaining the same effective switch operation.

In a preferred embodiment of the invention, surge protection gaps arelocated on each end of the switch so that surges entering eitherterminal will cause flashovers to ground rather than across the switchopen gap. Each protective gap consists of a lower rod electrodecooperating with the insulator cap as the upper electrode. These gapsare adjusted so that their flashover value is sufficiently below theflashover value of the switch open gap to insure line-to-groundfiashovers under certain surge voltage conditions.

When a surge protective gap on a switch breaks down as a result of surgevoltage, current will normally flow between the gap electrodes untilfault protective devices operate. The ionization of the air between thegap electrodes attendant to this arcing causes the atmosphere in thevicinity of the gap to become conducting. If this ionized gas cloudenters the space between the switch jaw and hinge, a subsequentfiashover of the switch open gap may result. Thus, in the preferredconstruction, the lower gap electrodes are located in a zone away fromthe switch open gap so that the insulator units of the switcheffectively shield the switch open gap from the intrusion of the cloudof ionized gas.

One preferred location of gap electrodes would be on the centerline ofthe switch and on the opposite side of the insulator units from theswitch open gap. In some structures, this may interfere with mechanicaland electrical connections to the switch terminals, and they can bedisplaced to other areas which are still removed from the switch opengap area.

Accordingly, a primary object of this invention is to provide a novelsurge protection electrode for disconnecting switches.

Another object of this invention is to provide a novel electrodeconstruction for disconnecting switches which permits a decrease in thelength of the switch open gap of the switch.

Another ob'ect of this invention is to provide a novel surge protectiongap for disconnecting switches which makes the switch less expensive andsmaller in dimension.

A further object of this invention is to provide a novel electrode fordisconnecting switches which is positioned on the end of the switchsupport and is shielded from the switch open gap by the insulator.

Another object of this invention is to provide a novel surge protectiongap for disconnecting switches which is an integral component of theswitch.

Another object of my invention is to provide an integrated coordinatedswitch which has a minimum blade length and still prevents open gapbreak down on the occurrence of surge voltage.

These and other objects of my novel invention will become apparent fromthe following description when taken in connection with the drawings, inwhich:

FIGURE 1 shows a side view of a typical disconnect switch which can beprovided with the novel protection gap of the invention.

FIGURE 2 is a top view of the switch of FIGURE 1 with the switchmechanism removed to illustrate the support insulators and the surgeprotection gap.

Referring now to FIGURES 1 and 2, I have shown a typical disconnectingswitch which is of the type set forth in U.S. Patent 2673902, issuedMarch 30, 1954, entitled Disconnect Switch to Gustave E. Heberlein andassigned to the assignee of the instant application, which isincorporated herein as a part of the instant specification. It is,however, noted that the novel structure of the invention is applicableto all types of disconnect switches. -In FIGURES 1 and 2, a base 10 ofchannel iron which may be at ground potential has connected theretothree elongated insulator stacks 12, 13 and 14 which have upperconductive caps 12a, 13a and 14a. respectively.

Insulator stacks 12 and 13 carry the hinge terminal 15 of the switch andthe switch blade 16 which is pivotally mounted to terminal 15. Hingeterminal 15 is electrically connected to caps 12a. and 13a. Insulator 12which is rotatable with respect to terminal 15 and is rotated byoperating handle 17 operates a crank mechanism 18 connected to blade 16.Insulator stack 14 carries a jaw contact 19 which is connected to cap14a. and terminal 20 whereby rotation of crank mechanism 13 rotatesblade 16 from the open position shown in FIGURE 1 to a closed positionin which the end of blade 16 engages contact 19.

The specific operation of the operating mechanism is 3 more fullydescribed in the above noted patent, and reference is made thereto forfurther details.

When the open gap insulation of the disconnecting switch is called uponto provide safety for personnel working on deenergized lines orequipment, it is essential that this insulation be adequate to withstandthe maximum surge voltage which it may encounter. Switches designed inaccordance with industry standards are required to provide a gap whichis 10 percent greater than the dry arcing distance of the supportinginsulators 12, 13 and 14 which will Withstand impulse ratings of theinsulators. This gives a high probability, but not absolute assurance,that any over-voltage applied to the switch will cause a dischargebetween the live parts and ground rather than across the open gap. Whereswitch gap insulation provides protection to personnel, proper surgeprotection must be installed to make certain that a switch does notencounter voltages in excess of the gap withstand value.

The provisions (1) that a metal-to metal switch gap be 10 percent inexcess of the arcing distance over the insulator, and (2) that the opengap withstand a voltage 10 percent in excess of the insulator withstandrating, provide no positive assurance of insulator fiashover preference,because of the influence of electric field conditions within the twogaps since the configuration of the electrodes plays a vital part. Itwill be noted that the sphere gap fiashover voltage is very much higherthan that for a rod gap of the same spacing. The characteristics ofswitch and insulator gaps fall generally between the characteristics ofrod and sphere gaps. If, on a particular switch, electric fieldconditions cause the insulator gap to more closely approach the spherecharacteristics, the insulators may easily develop more impulse strengththan the switch gap which is 10 percent larger.

Control of insulator characteristics can be provided when each switch isequipped with rod gaps adjusted to have a critical flashover equal tothe BIL (basic insulation level) rating of the switch.

In accordance with the present 'mvention, the switch open gap is madesubstantially smaller by providing, integral with the switch, anintentional controlled flashover gap across the insulators to electrodescarried on the base. Moreover, this gap is removed from the switch opengaps so that the switch open gap is unaffected by ionized gasesgenerated in the protective gap and can, therefore, be made close to itstheoretical small value. In so doing, the switch open gap may now bedecreased for a switch of a given rating so that the blade 17 isshortened, and the entire switch becomes smaller and more economical.

In the preferred embodiment of the invention, a pair of rod electrodes21 and 22 are mechanically and electrically connected to conductivestraps 23 and Z4 respectively which are electrically and mechanicallyconnected to grounded base 16 as by welding.

If now, there is a surge voltage on either terminal 19 or terminal 20due, for example, to a lightning stroke on the line containing theswitch, a break-down path is provided from electrode 12a whichterminates the upper portion of insulator stack 12 to electrode 21 orfrom terminal 14a which terminates the upper end of insulator stack 14to rod 22.

The gaps provided by electrode 12a to rod 21 and electrode 14a to rod 22are, of course, sufiicient to prevent break-down under normal voltageconditions on the line. They function, however, to permit easierbreak-down under surge voltage conditions so that flash-over occurs toground rather than across the switch open gap.

As is best seen' in FIGURE 2, the rod electrodes 21 and 22 may belocated somewhere within the zones indicated by lines 27 and 28respectively where they are substantially shielded from the switch opengap by insulators 12, 13 and 14- or substantially removed from theswitch open gap. That is to say, when there is a break-clown across thegaps to either rod electrode 2-1 or rod electrode 22, the gasesgenerated during arcing are in a zone which is away from the switch opengap. Further, the insulator units of the switch will effectively shieldthe switch open gap from the intrusion of the cloud of ionized gas andwill cool the ionized gases which come into contact with them.

While a preferred location of the gaps would be on the centerline of theswitch, they may be offset as shown so as to not interfere with existingstructural elements.

To illustrate the manner in which the invention causes substantialreduction in the size of a given disconnect switch, in a typicaldisconnect switch not provided with the gap electrodes of the invention,and designed to opcrate, for example, in a 115 kilovolt system, with 550kv. basic impulse level, the height of the insulators l2, l3 and 14 was43 /2 inches, while the switch open gap was 5 6 inches. The total weightof the single pole switch with 5" dia. BC. insulators was 1150 pounds.For this same duty, a switch having a switch open gap of only 44 inchesmay be provided when rod-type electrodes 21 and 22 are positioned asshown in FIGURE 1 external of, or removed from, the switch open gap. Thetotal weight of the single pole switch with 3 dia. BC. high-strengthinsulators is 650 pounds.

In the preferred embodiment of the invention, for 115 kv. switch ratingrods 21 and 22 were 8 /2 inches in height and formed of galvanized steelhaving a thickness of /8 inches.

The substantial reduction in the length of the switch open gap whenusing the invention has also been found to significantly reduce the costof the switch. Moreover, the operating characteristics of the switch arecompletely unaffected, even though there has been a substantial savingin cost and size.

Thus I have provided a completely coordinated switch which whenassembled by the manufacturer has made all necessary provision for opengap surge voltage protection with a minimum blade length.

Although l have described preferred embodiment of my novel invention,many variations and modifications will now be obvious to those skilledin the art, and I prefer therefore to be limited not by the specificdisclosure herein but only by the appended claims.

I claim:

1. A coordinated disconnect switch having a first terminal, a secondterminal, conductive means movable from a first position to a secondposition for electrically connecting and disconnecting respectively saidfirst and second terminals, and insulator means for supporting saidfirst and second terminals and said conductive means from a supportstructure; said first and second terminals defining a switch open gapwhen said conductive means is in its said second position; an electrodeon said support structure; said electrode being removed from said switchopen gap; said electrode defining a fiashover path from said firstterminal to said electrode which is preferable to the fiashover pathfrom said first terminal to said second terminal for surge voltages sothat said flashover path is flashed over by surge voltage before saidswitch open gap will flash over; said electrode being an elongated rod;at least a portion of said insulator means being interposed between saidswitch open gap and said electrode.

2. A high voltage coortinated disconnect switch comprising a jaw endterminal, a hinge end terminal, a conductive switch blade carried onsaid hinge end terminal and movable into and out of engagement withrespect to said jaw end terminal, support means, first insulator meansfor carrying said hinge end terminal from said support means, and secondinsulator means for carrying said jaw end terminal from said supportmeans; said jaw end terminal and said hinge end terminal defining aswitch open gap when said conductive switch blade is moved out ofengagement with respect to said jaw end terminal; and a first and secondelectrode mounted on said base; said first electrode being mountedadjacent said first insulator means in an area removed from said switchopen gap; said second electrode being mounted adjacent said secondinsulator means in an area removed from said switch open gap; said firstinsulator means being interposed between said first electrode and saidswitch open gap; st id second insulator means being interposed betweensaid second electrode means and said switch open gap; said first andsecond electrodes being elongated rods, said first electrode and saidjaw end terminal defining a first surge protection gap; said secondelectrode and said hinge end terminal defining a second surge protectiongap; said first and second surge protection gap defining fiashover pathswhich are preferred to said switch open gap under surge voltageconditions.

3. in a coordinated disconnect switch mounted on a grounded base andhaving two terminals; a first and second elongated rod electrode beingelectrically connected and mounted at each end of said base; said firstand second elongated rod electrodes being removed from the switch opengap area of said disconnect switch; said first and second elongated rodelectrodes defining first and second respective surge protective gapswith respect to terminals of said two terminals of said disconnectswitch; said first and second elongated rod electrodes beingindividually adjustably positioned in a 180 quadrant.

Nelson Sept. 12, 1939 Heberlein Mar. 30, 1954

3. IN A COORDINATED DISCONNECT SWITCH MOUNTED ON A GROUNDED BASE ANDHAVING TWO TERMINALS; A FIRST AND SECOND ELONGATED ROD ELECTRODE BEINGELECTRICALLY CONNECTED AND MOUNTED AT EACH END OF SAID BASE; SAID FIRSTAND SECOND ELONGATED ROD ELECTRODES BEING REMOVED FROM THE SWITCH OPENGAP AREA OF SAID DISCONNECT SWITCH; SAID FIRST AND SECOND ELONGATED RODELECTRODES DEFINING FIRST AND SECOND RESPECTIVE SURGE PROTECTIVE GAPSWITH RESPECT TO TERMINALS OF SAID TWO TERMINALS OF SAID DISCONNECTSWITCH; SAID FIRST AND SECOND ELONGATED ROD ELECTRODES BEINGINDIVIDUALLY ADJUSTABLY POSITIONED IN A 180* QUADRANT.